Poly vinyl acetate and its Derivatives

Because of its high cold flow, poly(vinyl acetate) is of little value in the forni of mouldings and extrusions. However, because of its good adhesion to a number of substrates, and to some extent because of its cold flow, a large quantity is produced for use in emulsion paints, adhesives and various textile finishing operations. A minor proportion of the material is also converted into poly(vinyl alcohol) and the poly(vinyl acetal)s which, are of some interest to the plastics industry. 

The lUPAC systematic name for poly(vinyl acetate) is poly-( 1-acetoxy-ethylene) and that for poly (vinyl alcohol) is poly-(l-hydroxyethylene). As with other common polymers the lUPAC names are not in general use. 

In addition to the above materials a number of copolymers containing vinyl acetate have been marketed. Ethylene-vinyl acetate (EVA) copolymers are discussed in Chapter 11 and vinyl chloride-vinyl acetate copolymers in Chapter 12. On the other hand, the commercial ethylene-vinyl alcohol copolymers, although derived from EVA, are considered briefly in this chapter since in weight terms the ethylene component is usually the minor one. 

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Poly(vinyl acetate) and its Derivatives CH,= CH, + 2CH,COONa + PdCL... 

Applications of Poly(vinyl acetate) and Its Derivatives. Poly-(vinyl acetate) homopolymers and high-VA-content copolymers are mainly used as emulsions. They are part of many compounds due to their adhesive properties. They are also the main component of vinyl paints indeed, their glass transition temperature is close to ambient, and their adhesive properties are particularly well-fitted to this application. 

Solution Polymerization. Solution polymerization of vinyl acetate is carried out mainly as an intermediate step to the manufacture of poly(vinyl alcohol). A small amount of solution-polymerized vinyl acetate is prepared for the merchant market. When solution polymerization is carried out, the solvent acts as a chain-transfer agent, and depending on its transfer constant, has an effect on the molecular weight of the product. The rate of polymerization is also affected by the solvent but not in the same way as the degree of polymerization. The reactivity of the solvent-derived radical plays an important part. Chain-transfer constants for solvents in vinyl acetate polymerizations have been tabulated (13). Continuous solution polymers of poly(vinyl acetate) in tubular reactors have been prepared at high yield and throughput (73,74). 

Tackifiers are used to increase the tackiness and the setting speed of adhesives. They increase tackiness by softening the poly(vinyl acetate) polymer in the wet and the dry adhesive film. Tackifiers are usually rosin or its derivatives or phenoHc resins. Other additives frequently needed for specific apphcation and service conditions are antifoams, biocides, wetting agents, and humectants. 

More than 500 million pounds of poly(vinyl acetate) (PVAc), poly(vinylidene chloride), and their copolymers and polymers derived from them are produced annually in the United States. PVAc does not have sufficient strength for producing the types of products obtained from polyethylene, polystyrene, and poly(vinyl chloride) since it is noncrystalline and has a Tg of only 28°C. However, poly(vinyl acetate) (XLI) and its copolymers find uses as... 

Syndiotactic polymers, as we have seen above, are stereoregular and so are crystallizable. They, however, do not have the same mechanical properties as isotactic polymers, because the different configurations affect the crystal structures of the polymers. Most highly stereoregular polymers of commercial importance are isotactic, and relatively few syndiotactic polymers are made. Atactic polymers, on the other hand, are usually completely amorphous unless the side group is so small or so polar as to permit some crystallinity. Thus, while atactic poly(vinyl acetate) has never been crystallized, poly(vinyl alcohol), which is derived from it and is also atactic, has been found to crystallize. 

For a given experimental pressure (or corresponding reduced pressure) and introducing the explicit expressions for the two free-energy derivatives, a partial differential equation for y ensues. Its solution provides the E T dependence of the free volume. It will be noted that y does not freeze at Tg but only exhibits a reduced temperature coefficient [McKinney and Simha, 1976]. In subsequent discussion, as in most applications, an approximation has been used that avoids the complications attendant on to Eq. (4.2a). That is, the first term on the right-hand side has been used together with an experimental pressure to solve for y as an adjustable quantity. A comparison with the result obtained from the full Eq. (4.2a) for the case of two poly(vinyl acetate) (PVAc) glasses shows this to be an acceptable approximation not too far below Tg. 

Polyvinyl compounds are produced either by the polymerization of vinyl compounds CH2=CHX or by polymer analog reactions on polyvinyl compounds. The derivatives of poly(vinyl alcohol) -%CH2—CH(OHH- , poly(vinyl halides) -f-CH2—CHHal and poly-(vinyl amines) -%CH2—CH(NRiR2)- are of particular commercial importance. In contrast to these, poly(vinyl sulfides) -f-CH2—CH(SR)- are only of academic interest. Vinyl alcohol is unstable, since it transforms into acetaldehyde on formation. Therefore, poly(vinyl alcohol) is produced from poly(vinyl acetate). 

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